Input devices including proximity sensor devices (also commonly called touchpads or touch sensor devices) are widely used in a variety of electronic systems. A proximity sensor device typically includes a sensing region, often demarked by a surface, in which the proximity sensor device determines the presence, location and/or motion of one or more input objects. Proximity sensor devices may be used to provide interfaces for the electronic system. For example, proximity sensor devices are often used as input devices for larger computing systems (such as opaque touchpads integrated in, or peripheral to, notebook or desktop computers, or as transparent sensor devices integrated with display screens to provide a touch screen interface).
Many proximity sensor devices use capacitive techniques to sense input objects. Such proximity sensor devices may typically incorporate either profile capacitive sensors or capacitive image sensors. Capacitive profile sensors alternate between multiple axes (e.g., x and y), while capacitive image sensors scan multiple transmitter rows to produce a more detailed capacitive “image” of “pixels” associated with an input object. While capacitive image sensors are advantageous in a number of respects, some implementations may be particularly vulnerable to various types of interference, including various types of noise.
Interference can originate from various sources, including display backlights, power supplies, wireless communication devices and the like. Although many sensors now include filtering that can effectively remove many types of interference, problems remain in identifying and/or removing some types of interference. One type of interference that may be problematic in some proximity sensor devices is referred to as “unison noise”. One typical source for unison noise in some sensor devices is a nearby display screen, such as a liquid crystal display (LCD) used in many touch screen implementations.
In general, unison noise is a type of interference that is relatively spatially uniform over the sensing region, but varies nearly randomly over time. Specifically, because many image type sensor devices receive signals on a row-by-row or column-by-column basis, with each row or column receiving signals at different moments in time, each row or column in the sensor data can be uniformly shifted up or down by random amounts. This results in row-to-row or column-to-column variations that can negatively impact the performance of an image proximity sensor device.
Thus, while capacitive image proximity sensor devices are advantageous in a number of respects, there is a continuing need to improve the performance of such devices. For example, to improve the responsiveness of such sensors, or to improve the sensor's resistance to various types of interference, including various types of unison noise.
Other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.